Gas turbine engines which are intended for industrial or marine use are typically adapted to drive a power turbine through an interturbine duct. Thus the exhaust efflux nozzle of the engine is connected to the inlet of a power turbine by the interturbine duct. The interturbine duct must, of course, .have to withstand the high temperatures associated with the efflux of a typical gas turbine engine and so, can be made in single skin form from an exotic heat resistant alloy such as a nickel based alloy. However such alloys tend to be expensive and other drawbacks associated with the possible consequences of any structural failure of the duct or the leakage of hot, corrosive exhaust gases from the connecting joints of the duct, tend to discourage their use.
An alternative approach is to manufacture the interturbine duct from cheaper, less exotic alloy and cool the duct with, for instance, air tapped from the compressor of the gas turbine engine. However typical methods of providing duct cooling usually entail the use of large numbers of ducts and baffles which unfortunately are prone to failure as a result of the considerable buffetting, vibration and thermal fatigue which they would be likely to encounter in normal use.
It is an object of the present invention to provide a cooled interturbine duct which substantially avoids the drawbacks referred to above.